Hi Alvaro,
The green screen means that the built-in kernel driver is loading
successfully for your device, but higher level X configuration to make
use of it is both difficult and limited on Linux. It's often not
possible to get a 2nd or 3rd screen configured (especially if you'd
like to span multiple PCI and USB adapters). See here for more
detail:
http://plugable.com/2011/12/23/usb-graphics-and-linux
For this reason, we don't recommend buying these for Linux unless
you're doing a specific scenario that has a single display per USB
graphics device (like automatic USB multiseat; or a single monitor on
an embedded system).
I'm sorry for the bad news! Plugable tries to be good about customer
support. If you email support at plugable.com and say if you don't have a
Windows, Mac, or single-monitor Linux system to use it with, you can
get help with a refund.
Best wishes,
Bernie